FEATURE CUT: HTML5ed image output moved to Toolbox module

The deleted file contained functions that wrapped images in <figure>
elements when thy were send to the editor. Also the native gallery
output was HTML5ed with <figure> and <figcaption>. Since that kind of
functionality shouldn't be theme related, but maintainable through an
eventual theme change, those functions have been moved to a Tooblox
module. Get it here: https://github.com/glueckpress/modules